Matrix type display devices such as an LCD (Liquid Crystal Display), an EL (Electroluminescence) display device, and the like are frequently used as various display devices that are light weight, thin, and have high image quality and high definition. A matrix type display device comprises matrix-formed bus lines, an optical material (luminescent material or light modulation material), and if required, other components.
In a monochromatic matrix type display device, wiring and electrodes must be arranged in a matrix on the display substrate, but the optical material can be uniformly coated over the entire surface of the display substrate.
In contrast, for example, when a so-called matrix type color display device is realized by using an EL display device of the type that emits light by itself, it is necessary to arrange three pixel electrodes corresponding to the primary colors RGB of light for each pixel, and coat the optical material corresponding to any one of the primary colors RGB for each pixel electrode. Namely, the optical material must be selectively arranged at the predetermined positions.
There is thus demand for developing a method of patterning the optical material. Suitable examples of effective patterning methods include etching and coating.
First, a layer of an optical material is formed over the entire surface of the display substrate. Then a resist layer is formed on the optical material layer, exposed to light through a mask and then patterned. Then the optical material layer is patterned by etching in correspondence with the resist pattern.
However, in this case, a large number of steps are required, and each of the materials and apparatus used is expensive, thereby increasing the cost. Also a large number of steps are required, and each of the steps is complicated, thereby deteriorating throughput. Further, depending upon chemical properties, some optical materials have low resistance to resist and an etchant, and thus these steps are impossible.
On the other hand, the coating process is carried out as follows.
First, an optical material is dissolved in a solvent to form a solution, and the thus-formed solution of the optical material is selectively coated at the predetermined positions on the display substrate by an ink jet method or the like. Then, if required, the optical material is solidified by heating, irradiation of light, or the like. In this case, a small number of steps are required, and each of the materials and apparatus used is inexpensive, thereby decreasing the cost. Also, a small number of steps are required, and each of the steps is simple, thereby improving throughput. Further, these steps are possible regardless of the chemical properties of the optical material used as long as a solution of the optical material can be formed.
The coating patterning method is thought to be easily carried out. However, as a result of experiment, the inventors found that in coating the optical material by the ink jet method, the optical material must be diluted at least several tens of times with a solvent, and thus the solution obtained has high fluidity, thereby causing difficulties in holding the solution at the coating positions until it is completely solidified after coating.
In other words, patterning precision deteriorates due to the fluidity of the solution of the optical material. For example, the optical material coated in a pixel flows to the adjacent pixels to deteriorate the optical properties of the pixels. Also variations occur in the coating areas in the respective pixels, thereby causing variations in the coating thickness and thus the optical properties of the optical material.
Although this problem significantly occurs with an optical material for EL display devices or the like, which is liquid during coating and then solidified, the problem also occurs in cases in which a liquid crystal that is liquid both during and after coating is selectively coated on the display substrate.
The present invention has been achieved in consideration of the unsolved problem of the prior art, and an object of the invention is to provide a matrix type display device in which a liquid optical material can securely be arranged at predetermined positions while maintaining characteristics such as low cost, high throughput, a high degree of freedom of the optical material, etc., and a manufacturing method thereof.